Methods of handling wind turbine blades and mounting said blades on a wind turbine, system and gripping unit for handling a wind turbine blade

ABSTRACT

The invention relates to methods of handling wind turbine blades and mounting said blades on a wind turbine, said method comprising the steps of lifting a wind turbine hub to the nacelle of wind turbine with a lifting system and mounting the hub on the nacelle. Further, the method comprises the steps of gripping at least one wind turbine blade with a lifting system including at least one gripping unit for handling wind turbine blades, lifting said at least one wind turbine blade into close proximity to said hub, and mounting said at least one wind turbine blade on said hub. 
     The invention also relates to a gripping unit for handling a wind turbine blade during transport.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims the benefit of, U.S.application Ser. No. 10/503,192 filed on 30 Jun. 2004, the entirecontents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to methods of handling wind turbine blades andmounting said blades on a wind turbine, and a system and gripping unitfor handling a wind turbine blade.

Modern wind turbines usually comprise a rotor with a considerablediameter and weight, as illustrated in FIG. 1. The diameter of modernrotors is approaching 100 to 150 meters and the rotor including the windturbine hub and e.g. three wind turbine blades may add up to around 40to 50 tons.

The usual way of mounting a wind turbine includes the steps oftransporting the different elements to the site of the wind turbine,assembling the tower sections and the tower, lifting the wind turbinenacelle with a crane and mounting the nacelle on top of the tower,assembling the wind turbine rotor on the ground, and lifting the windturbine rotor with the crane and mounting the rotor to the low speedshaft extending from the nacelle.

The usual way comprises a number of disadvantages which have become moreand more problematic with the increasing size and weight of the windturbine rotor.

Especially assembly of the wind turbine rotor on the ground isproblematic as it requires a large area free of obstacles, which isplanar and stable in order to be accessible for the assembly workers andthe crane. With a rotor diameter of 100 meters, the area in questionmust exceed 5000 m2.

Further, lifting of the rotor to the nacelle is rather complicated, asthe rotor must be turned 90 degrees in midair.

In other lifting systems, it is known to pre-mount the wind turbine hubon the nacelle and then lift each wind turbine blade successively to aposition next to hub and perform the mounting of the blades. The liftingis performed with the wind turbine blades lying in a number of slings.

This lifting system comprises a number of disadvantages and one of themis the fact that the blade has to be horizontal during lifting andmounting.

Further, the blade has to be positioned with the front facing downwardsto the bottom of the slings in order not to be damaged. This only allowsmounting of the blade on the hub in a production position which meansthat the hydraulic pitch system of the wind turbine has to be manuallyoverruled and mechanical break force to be added to the low-speed axleof the turbine in order to keep the rotor system from rotating duringmounting.

BRIEF SUMMARY OF THE INVENTION

The invention establishes a wind turbine without the above-mentioneddisadvantages.

Especially, the invention establishes a lifting system which is flexibleand easy to use on many geographic sites regardless of the surroundings.

In accordance with the invention, a method of handling wind turbineblades and mounting said blades on a wind turbine is stated, said methodcomprising the steps of:

lifting a wind turbine hub to the nacelle of a wind turbine with alifting system and mounting the hub on the nacelle or lifting the windturbine hub and the nacelle together with a lifting system and mountingthe nacelle, including the hub, on a wind turbine tower,

lifting at least one wind turbine blade with a lifting system forhandling wind turbine blades,

lifting said at least one wind turbine blade into a vertical positionbelow and in close proximity to said hub, and mounting said at least onewind turbine blade on said hub.

Hereby, it is possible to handle and mount a wind turbine blade in anadvantageous manner.

Especially, the possibility of lifting the wind turbine blade to aposition below the hub instead of to a higher position is advantageousas this allows the use of cranes with a lower maximum height. The cranecosts are increased significantly with the otherwise required maximumheight.

In an embodiment of the invention, lifting of at least one wind turbineblade is performed from an initial position which is substantiallyhorizontal in relation to the longitudinal axis of the blade to a finalposition which is substantially vertical and in close proximity to saidhub. Hereby, it is possible to lift the wind turbine blade from ahorizontal position e.g. on the ground or on the deck of a ship to avertical mounting position.

In a further embodiment of the invention, at least one wind turbineblade is mounted on said wind turbine hub before lifting of the hub andat least one wind turbine blade is mounted on said wind turbine hubafter lifting of the hub. Mounting on the ground of at least one windturbine blade, e.g. two blades on the hub, is advantageous and onlypossible since the blades may point upwards during mounting and lifting.

In an even further embodiment of the invention, at least the mounting ofsaid at least one wind turbine blade on said hub is performed with theblade in a substantially vertical position. By lifting the blade to avertical position, it is possible to lift the blade into a position justbelow the bar/jip of the crane and use the crane more efficiently bylifting the blade higher which allows for a smaller crane to perform thesame lift.

In a fourth embodiment of the invention, lifting and mounting of saidwind turbine blade is performed with the blade in non-productionposition in relation to the wind. The blade in a non-production positionin relation to the wind is to be understood as the front (or tail) ofthe blade facing the wind whereby any pull from the wind is avoided.

Hereby, it is possible to lift and mount the wind turbine blades duringhigher wind speeds than the known systems since mounting in anon-production position is feasible. Further, it is not necessary toturn one or more of the blades during the mounting.

The yaw mechanism of the nacelle will keep the wind turbine turnedagainst the wind.

In a fifth embodiment of the invention, lifting is performed with agripping unit gripping said wind turbine blade. By using a grippingunit, the blade is easier to control during lifting and this allows forvertical lifting.

In a sixth embodiment of the invention, lifting from a substantiallyhorizontal to a final vertical position is enhanced by a lever arm and aweight attached to the gripping unit. By using a lever arm and a weightattached to the gripping unit, it is possible to create a gripping unitwhich is forced by gravity to make a rotating movement from horizontalto vertical position and thus enhance control of the blade as the weightcenter point of the system is moved away from the blade and the liftingpositions on the blade.

In a seventh embodiment of the invention, the gripping unit grips a windturbine blade in at least two lifting positions.

In an eighth embodiment of the invention, the gripping unit performs thegrip by forcing a number of clamping jaws against the sides of the windturbine blade in at least two lifting positions. By using clamping jawsagainst the side of the blade it is possible to obtain a large contactsurface.

In a ninth embodiment of the invention, the gripping unit grips a windturbine blade in at least two lifting positions, said lifting positionsbeing symmetrically positioned around the center point of said windturbine blade.

In a tenth embodiment of the invention, lifting of said at least onewind turbine blade is performed by at least one crane lifting saidgripping unit in said at least two lifting positions. By using at leasttwo lifting positions, lifting safety is enhanced.

In an eleventh embodiment of the invention, said at least one windturbine blade is controlled by one or more wires connected to said craneor to one or more winches. By using one or more wires to control theblade, lifting safety is enhanced.

In accordance with the invention, a further method of handling windturbine blades and mounting said blades on a wind turbine is stated,said method comprising the steps of:

lifting a wind turbine hub to the nacelle of a wind turbine with alifting system and mounting the hub on the nacelle or lifting the windturbine hub and the nacelle as one with a lifting system and mountingthe nacelle, including the hub, on a wind turbine tower,

gripping at least one wind turbine blade with a lifting system includingat least one gripping unit for handling wind turbine blades,

lifting said at least one wind turbine blade into close proximity ofsaid hub, and mounting said at least one wind turbine blade on said hub.

Hereby, it is possible to handle and mount a wind turbine blade in anadvantageous manner.

In accordance with the invention, a system for handling wind turbineblades and mounting said blades on a wind turbine is stated, said systemcomprising a gripping unit for a wind turbine blade and a liftingsystem.

By using gripping means in relation to lifting a wind turbine blade, itis possible to perform the lift in a flexible and easy manner. Further,the risk of damage to the blade during lifting is reduced significantlyas control of the blade is enhanced in a lifting action involvinggripping of the blade.

In an embodiment of the invention, said lifting system includes a cranewith a number of wires lifting and controlling said gripping unit.Hereby, an easy and safe lifting operation is made feasible.

In a further embodiment of the invention, at least one additional wirecontrolling said at least one wind turbine blade is connected to saidblade with connection means such as a flexible cuff or a similarflexible band surrounding part of the tip of said blade. By establishingwired control points, e.g. at the outer ends of the blade being lifted,it is possible to control the blade more efficiently which allowslifting and mounting of wind turbine blades at higher wind speeds.Further, lifting and mounting may be less troublesome and quicker whichreduces the required manpower and the costs in general.

In accordance with the invention, a gripping unit for handling a windturbine blade is stated, said unit comprising gripping means. By usinggripping means in relation to lifting of a wind turbine blade, it ispossible to perform the lift in a flexible and easy manner. Further, therisk of damaging the blade during lifting is reduced significantly ascontrol of the blade is enhanced in a lifting action involving grippingof the blade.

In an embodiment of the invention, said gripping means comprises atleast two gripping points. By using at least two gripping points, apreferred relation between functionality and safety in relation to thelifting is achieved.

In a further embodiment of the invention, said gripping means comprisesa curved surface following the shape of specific types of wind turbineblades. By adapting the surface shape of the gripping means to aspecific type of wind turbine blade, it is possible to achieve a morefirm and long-lasting grip of the blade and thus increase safety duringlifting.

In an even further embodiment of the invention, the position of saidgripping means is connected to a hydraulic, an electric or a pneumaticsystem for stepless adjustment of the position of the gripping means inrelation to said wind turbine blade.

In a fourth embodiment of the invention, said gripping means may bechanged from one size to another. The gripping jaws are hereby easilyreplaceable and are matched to suit the blade type to be handled.

Further, a wide gripping range is made possible.

In a fifth embodiment of the invention, said gripping means includesclamping jaws engaging with the surface of a wind turbine blade. Byusing clamping jaws, it is possible to apply extensive gripping force tothe wind turbine blade in a controlled manner. Especially, it ispossible to monitor the pressure that the clamping jaws place on theblade by measurements in the mechanical or hydraulic system associatedwith the clamping jaws and limit the force transferred onto the blade.Further, it is possible to ensure minimum force used in connection withgripping the blade.

In a sixth embodiment of the invention, said gripping means includes atleast one stepless adjustable clamping jaw and at least one fixedclamping jaw, said jaws forming a clamping jaw set. By using pairs ofclamping jaws comprising a fixed and a movable jaw, it is possible tocreate gripping means with less components performing the movements butwith the same functionality as a system with pairs of movable jaws. Byhaving fewer components perform the movements, improved operationalreliability of the gripping means is ensured. Further, the cost of thegripping means is reduced as only one of the more complicated movablejaws is needed in a pair. By allowing the movable jaws to be adjustablein steps, it is possible to hold the blade in a firm grip regardless ofthe conditions e.g. a wet surface of the blade or the like.

Further, a wide gripping range is made possible.

In a seventh embodiment of the invention, said clamping jaws includes afriction surface layer. The condition of the wind turbine blade surfacemay be anything from soaking wet to perfectly dry and as such theclamping jaws must be prepared for the different conditions. By using afriction surface layer, it is possible to maintain the grip of the bladewithout having to increase the grip force e.g. if the blade surfacebecomes wet.

In an eighth embodiment of the invention, said friction surface layercomprises vulcanized rubber. Hereby, it is possible to avoid or at leastminimize jaw marks on the wind turbine blade as the vulcanized rubberwill protect the blade surface. In order to achieve max. productioncapacity from a wind turbine, it is important that the mounted windturbine blades are without faults or marks. Further, the vulcanizedrubber will ensure a firm grip of the blade regardless of the bladeconditions as mentioned above.

In a ninth embodiment of the invention, said friction surface layercomprises at least one tread pattern. By using a tread pattern, e.g.known from vehicle tires, it is possible to maintain a firm grip of awind turbine blade and further have rain or other moisture directed awayfrom the contact surfaces between the jaws and the blade.

In a tenth embodiment of the invention, said at least one tread patternincludes one or more dents. By using dents, it is possible to direct andcollect raindrops or other moisture in central places positioned awayfrom the contact surfaces between the jaws and the blade.

In an eleventh embodiment of the invention, said clamping jaws includeone or more vertical ribs. The clamping jaws are particularly exposed topressure by the blade in a direction perpendicular to the longitudinalaxis of the blade and as such, it is advantageous to add vertical ribsto the jaws, e.g. steel bars mounted on the back of the jaw surfacefacing the blade.

In a twelfth embodiment of the invention, said unit comprises two setsof jaws symmetrically positioned around the center point of a windturbine blade.

The center point of the blade is the mass center point of the blade (orthe blade and the gripping unit) in a direction perpendicular to thelongitudinal axis of the blade. By positioning the sets of jawssymmetrically around the center point, less effort is required to turnthe blade from one position to another e.g. from horizontal to verticalposition.

In a thirteenth embodiment of the invention, said unit comprises anumber of jaws sets, said sets being adapted to a given wind turbineblade type. In order to obtain a firm grip of the blade (and thusincrease safety), it is crucial that the jaws are adapted to the windturbine blade type being lifted.

Further, a wide gripping range is made possible.

In a fourteenth embodiment of the invention, said unit comprises twosets of clamping jaws. By using two sets of clamping jaws, a preferredrelation between cost, functionality and safety of lifting is achieved.

In a fifteenth embodiment of the invention, said unit comprises a leversystem comprising a lever arm and at least one weight. By using a leversystem, it is possible to move the mass center of the wind turbine bladeand gripping unit as one closer to the lifting positions and thusenhance control of the movement as well as make it easier on the leversystem due to the force of gravity.

In a sixteenth embodiment of the invention, said lever system furthercomprises a hinge allowing the lever arm and at least one weight to bemoved from a lifting position to a transportation position. Hereby, itis possible to create a gripping unit with a lever system which iscompact during transport. In the transport phase, it is very importantto keep the dimensions of the gripping unit compact in order to allowstandardized transport such as container transport.

In a seventeenth embodiment of the invention, said lever systemcomprises a number of movable bolts connected to said hinge. By usingmovable bolts, it is possible to convert the gripping unit from useposition into transportation position in an easy manner by means ofstandard tools.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in the following with reference to thefigures in which

FIG. 1 shows a large modern wind turbine,

FIGS. 2 a to 2 c show the different steps of lifting and mounting windturbine blades according to the invention,

FIG. 3 a shows a preferred embodiment of a gripping unit according tothe invention,

FIG. 3 b shows a magnified section of FIG. 3 a,

FIG. 3 c shows a front view of the preferred embodiment of the grippingunit and magnified sections of the figure,

FIG. 3 d shows a top view of the preferred embodiment of the grippingunit,

FIG. 3 e shows the preferred embodiment of the gripping unit in relationto a center point of the wind turbine blade,

FIG. 3 f shows a preferred embodiment of a clamping jaw seen from theside and the front,

FIGS. 4 a to 4 c show different positions of the preferred embodiment ofthe gripping unit,

FIG. 5 shows a preferred embodiment of the gripping unit with the leversystem in transport position, and

FIG. 6 shows a flow chart of the functionality of a preferred embodimentof a lifting system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a modern wind turbine 1 with a tower 2 and a wind turbinenacelle 3 positioned on top of the tower. The wind turbine rotor 5 isconnected to the nacelle through the low speed shaft 6 extending fromthe nacelle front (shown in FIG. 2 a).

As illustrated in the figure, winds over a certain level will activatethe rotor and allow it to rotate perpendicularly to the wind. Therotation movement is converted into electric power which is usuallysupplied to the transmission grid as will be known by persons skilledwithin the area.

The FIGS. 2 a to 2 c show the different steps of lifting and mounting awind turbine hub and three wind turbine blades according to a preferredembodiment of the invention. The wind turbine may be an on-shore or anoff-shore wind turbine in which the different positions cause differentproblems such as the ground space within which the mounting of the rotorcan be performed.

FIG. 2 a shows a crane 7 lifting the rotor 5, said rotor comprising twowind turbine blades and wind turbine hub 4. The hub and the two bladesare assembled on the ground and then lifted to the same height as thewind turbine nacelle 3 and in close proximity to the low speed shaft 6extending out of the nacelle, so that they may be connected to eachother.

The hub and the two wind turbine blades are maintained in a lockedposition with the last assembly opening for a wind turbine blade facingdownwards and the two blades pointing upwards. The wind turbine bladesare faced against the wind in a no production position.

FIG. 2 b shows the crane 7 lifting the last wind turbine blade 8 fromthe ground toward the rest of the rotor 5. The blade is positioned in agripping unit 10 close to its root end. The gripping unit 10 is shapedas a yoke which partly surrounds the wind turbine blade 8. The yokeincludes a number of clamping jaws which may engage with the blade.

The gripping unit 10 also comprises a lever arm 11 with a weight at thefree end of arm. The lever arm 11 is connected to the gripping unit 10at the back of the gripping unit 10 and the back of the gripping unit isfacing the tip of the wind turbine blade.

The gripping unit 10 is suspended in number of places with a number ofcrane wires 12, 13, 14.

The first wire 13 is connected to the front of the gripping unit 10 andthe front of the gripping unit is facing the root of the wind turbineblade.

The second wire is connected to the free end of the lever arm 11 at theback of the gripping unit 10.

The first and second wires are also connected to the crane 7 through twoseparate positions on a crane bar/jip 15 above the blade. With the cranemotor and the two different wires, it is possible to rotate the bladefrom a horizontal position into a vertical position (as shown in FIG. 2c).

The third wire 14 is also connected to the free end of the lever arm 11at the back of the gripping unit 10. The wire is also connected to themain body of the crane and is usually vertical but moves into horizontalduring lifting. With the crane motor and the wire, it is possible tocontrol the blade 8 and keep it from moving horizontally when it is notrequired.

FIG. 2 c further shows the wind turbine blade 8 lifted to a positionjust below the wind turbine 1 at the assembly opening in the hub 4. Theblade is faced against the wind in a non-production position.

The assembly workers previously having assembled the hub and the lowspeed shaft may perform the assembly of the blade 8 and the hub 4 in anormal manner.

After the assembly of the blade 8 and the hub 4, the rotor is completeand the locking means may hereafter be removed in order to allow thewind turbine to start energy production.

During lifting of the blade from a horizontal position into a verticalposition, the lever arm 11 and the weight make it easier to control theblade 8.

In a preferred embodiment of the invention, lifting of the blade isperformed with further control wires being connected to the blade, e.g.with a flexible cuff or a similar flexible band surrounding part of thetip of said blade. The wires may be controlled with winches on theground or positioned on the crane and used to control the movement ofthe blade, e.g. control the position of the blade tip during lifting.

In an alternative embodiment of the invention, the hub with the twoblades is mounted on the nacelle and the crane lifts the nacelle and thehub with the blades in one lift to the top of the wind turbine tower.Hereafter, the last wind turbine blade is lifted with the gripping unit10 just below the hub in the vertical position and the blade is mountedon the hub.

FIG. 3 a shows a preferred embodiment of a gripping unit 10 according tothe invention. The gripping unit 10 comprises a number of steel barsperpendicularly connected in order to create a yoke capable ofsurrounding the wind turbine blade 8.

In the four-sided window created by the steel bars, a section ofelectric accumulators 20 supplying the necessary electric power for ahydraulic system, the control systems and other systems needing electricpower is mounted. Some of the hydraulic components and control systemsare positioned in the control box or cabinet 21. The hydrauliccomponents may be a hydraulic tank containing hydraulic oil and ahydraulic pump supplying hydraulic pressure to the rest of the hydraulicsystem. The necessary electric power to the electric motor driving thehydraulic pump is supplied from the electric accumulators 20.

The lever arm 11 may be constructed as two separate arms extending fromthe gripping unit 10 and with the free ends of the arms being connectedto the weight 17 as a bar between the arms.

The weight 17 may be comprised by a number of different materials suchas concrete blocks or metal plates e.g. lead plates. The weight may alsobe made (more or less) solidly in a heavy metal such as steel.

In a preferred embodiment, the total mass of the weight 17 is between 1and 5 tons such as approximately 2.2 tons.

FIG. 3 b shows a magnified section of FIG. 3 a in relation to thegripping unit 10. The section includes a first and a second barconnected to a furnishing 22 in a perpendicular connection establishingone corner of the yoke surrounding the wind turbine blade 8.

Close to the perpendicular connection, the second gripping mechanism16-II is positioned. The second gripping mechanism 16-II includes ahydraulic actuator 18 and a backup actuator 19 whose ends may be seen inFIG. 3 b. The rods of the actuators 18, 19 are connected to a clampingjaw that may be pushed against the side of the wind turbine bladepositioned within the yoke of the gripping unit 10.

The two actuators 18, 19 are of the same type, have the same connectionto the hydraulic system and thus have the same functionality. If thehydraulic actuator 18 fails, the backup actuator will still hold theclamping jaw and thus the wind turbine blade 8.

FIG. 3 c shows a front view of the preferred embodiment of the grippingunit 10.

The yoke surrounding the wind turbine blade comprises a number of barsb4, b7, b8 connected by furnishings 22.

The first crane wire 13 is connected to the front of the gripping unit10 through a traverse system comprising a first connection eyelet 25 andtwo wires stretched over a traverse bar 24 and connected to oppositesides of the gripping unit 10.

The figure further shows the lever arm 11 constructed as two separatearms extending from the gripping unit 10 with the free ends of the armsbeing connected with the weight 17 as a bar between the arms.

On top of the weight 17, the second connection eyelet 26 is positioned.The eyelet is used for connections of second and third crane wires 12,14.

In the lever arm, close to the connection point with the yoke of thegripping unit 10, a hinge 23 is incorporated. The hinge allows the leverarm and the weight 17 to be moved from an upright lifting position to afold-down transportation position and vice versa.

The magnified sections of the figure show the first and most of thesecond clamping jaw in a set 28 a, 28 b.

The first clamping jaw is stepless and movable towards one side of awind turbine blade. The hydraulic actuator and the backup actuator 18,19, establish the movement of the first clamping jaw 28 a. The movementof the actuators may be controlled and ultimately stopped by a hydraulicpressure valve indicating that the first clamping jaw has reached thewind turbine blade and is pushing it against the passive second clampingjaw 28 b at a certain force.

The second clamping jaw is fixedly connected to the gripping unit 10 butin a changeable manner e.g. by providing the rod 30 connecting the jawand the gripping unit 10 with a screw thread. The rod may be positionedin a given fixed position but if the clamping jaw or the position of theclamping jaw needs to be changed, this may be achieved by screwing therod partly or totally out of the gripping unit 10. The clamping jaw canbe changed if different types of blades with e.g. other dimensions thanthose of the previously lifted blades are to be lifted.

The gripping unit 10 further comprises a rubber surface 31 or a similarsurface on the bar side facing down against the top of the wind turbineblade. The rubber surface protects the blade against damage duringtransport and lifting.

The front of the first and second clamping jaws 28 a, 28 b may also beseparated from the rest of the clamping jaw system by removing the frontfrom the rods 37 and replacing them with another front having otherdimensions.

FIG. 3 d shows a top view of the preferred embodiment of the grippingunit 10 with the wind turbine blade 8 positioned inside the yoke definedby the gripping unit 10.

The figure shows three bars b1, b2, b3 parallel with the blade. Thefirst and third bars b1, b3 are positioned above the blade on oppositesides of the wind attack edge 33 of the blade. The second bar ispositioned above the wind attack edge 33 of the blade. The three barsb1, b2, b3 are connected by two perpendicular bars b4, b5 at both endsof the bars by means of furnishings 22.

As shown in FIG. 3 a, the bar structure is continued down the sides ofthe gripping unit 10 and thus creates a rigid yoke structure gripping awind turbine blade.

FIG. 3 e shows the preferred embodiment of the gripping unit 10 inrelation to the center point 34 of the wind turbine blade 8. The centerpoint is the transverse mass center of the wind turbine blade.

As shown, the two clamping jaws are positioned on opposite sides of thecenter point and substantially at the same distance from the centerpoint. The gripping unit 10, including the lever arm 11 and the weight17, will be in balance with the wind turbine blade when in verticalposition.

The upper side of the gripping unit 10 further shows a second connectioneyelet 26 and a third connection eyelet 32 used for connection of thecrane wires 12, 13, 14.

The wind turbine blade 8 is shown with the blade tip positioned to theleft and the blade root to the right (but outside the figure).

FIG. 3 f shows a preferred embodiment of a clamping jaw 28 according tothe invention in which the clamping jaw is seen from the side and thefront.

The clamping jaw 28 comprises one or more steel plates shaped to meet agiven surface of a wind turbine blade type in a specific position on theblade. In the shown figure, the clamping jaw 28 comprises an upper andlower plate welded together at an angle substantially meeting thesurface of the wind turbine blade.

To ensure the necessary rigidity of the clamping jaw 28 in the verticaldirection, it has a number of strengthening ribs 36. The ribs basicallyhave the same height as the clamping jaw 28 and are welded onto the backof the jaw at a certain distance between the ribs. In anotherembodiment, the strengthening of the clamping jaw 28 is obtained by onelarge rib mounted on the back of the jaw.

The clamping jaw 28 is also covered with a friction surface toward thewind turbine blade in order to secure a firm grip of the blade. Thefriction surface may be vulcanized rubber with a tread pattern 35 tofurther ensure a firm grip of the blade without making marks on it. Thethread pattern 35 includes one or more dents which will catch any waterdrops or moisture from the surface of the wind turbine blade or thesurroundings in general. By catching the water in dents, it is ensuredthat the water does not weaken the ability of the friction surface tohold on to the wind turbine blade as the water is kept away from thefriction surface.

The thread pattern 35 may be a pattern similar to the patterns knownfrom vehicle tires, such as rain tires, with patterns developed forleading rain away from the friction surface in an improved manner.

FIGS. 4 a to 4 c show different positions of the preferred embodiment ofthe gripping unit 10 during lifting of a wind turbine blade.

FIG. 4 a shows the gripping unit 10 in a substantially horizontalposition which is the initial position when lifting the wind turbineblade from the ground to the final assembly position.

In the present horizontal position, the wind turbine blade has just beenlifted from the ground or from a truck, a ship or another means oftransportation delivering the blade to the wind turbine site.

As shown, the first and second crane wires 12, 13 are substantiallyvertical and the third crane wire 14 is substantially horizontal. Thefirst and second crane wires 12, 13 lift the gripping unit 10 and thewind turbine blade 8. The two are initially lifted above ground whilekept in a substantially horizontal position.

The third crane wire 14 ensures that the lifted items are kept undercontrol in a horizontal plane.

FIG. 4 b shows the gripping unit 10 and a wind turbine blade 8 in alater situation than that of FIG. 3 a.

As shown, the first crane wire 12 pulls harder at the front of thegripping unit 10 than the second crane wire 11 at the back of thegripping unit 10. The gripping unit 10 and the blade 8 thus turn and areno longer horizontal.

The lever arm and the weight support the turn, as gravity will pull themdown and thus boost the turn.

FIG. 4 c shows the gripping unit 10 and the wind turbine blade 8 in thefinal vertical position. The turn has reached its end and the blade isready to be assembled with the wind turbine hub.

FIG. 5 shows the gripping unit 10 with the lever system 11, 17 in atransport position.

The transport position allows a compact system with less distancebetween the mass centers of the wind turbine blade 8 and the grippingunit 10.

The transportation position is obtained by opening the hinge 23,lowering the lever arm 11 and the weight 17 to the top of yoke andfastening the lever arm 11 and the weight 17.

FIG. 6 shows a flow chart of the functionality of a preferred embodimentof a lifting system according to the invention.

The lifting system includes a mechanical, a hydraulic and an electricsystem.

The mechanical system includes a first clamping jaw 28 a (No. I) andanother first clamping jaw 28 a (No. II) actively pressing against oneside of a wind turbine blade 8 in two different positions. On the otherside of the blade, two second clamping jaws 28 b passively create thenecessary counter pressure on the first set of clamping jaws 28 a.

At the same time, the first clamping jaw 28 a (No. I) is moved andcontrolled by a hydraulic actuator 41 and a backup actuator 42.

The actuators are part of a hydraulic system 44 which comprises ahydraulic pump 39 pumping hydraulic oil from a hydraulic tank 43 to thehydraulic actuators and the backup actuators moving and controlling theclamping jaws 28 a (Nos. I and II).

Pressure valves 40 control the pressure allowed by the hydraulicactuators and the backup actuators. By controlling the pressure at theactuators, and thus the clamping jaws, it is possible to control theholding force on the wind turbine blade.

The electric system 38 includes an electric motor driving the hydraulicpump as well as electric accumulators 20 supplying the necessaryelectric power to the motor and other components in the electric system.

Other embodiments of the lifting system may be established within thescope of the invention.

The lifting unit with the lever arm and at least one weight may be movedsubstantially 90 degrees in movement, from lifting position intotransportation position.

To achieve max. moment of force during lifting, it is important that theweight is positioned as far away from the blade as possible and that thelifting unit with the lever arm and the weight are as compact aspossible during transportation. In order to meet these requirements, itis advantageous to have the lever arm and the weight moved from aposition of close proximity to the blade (0 degrees in relation to theblade) to a position as far away from the blade as possible (90 degreesin relation to the blade). In a further embodiment, the lever system mayperform a stepless movement from a transportation position to a liftingposition or from one lifting position to another. The embodiment mayrequire control of the moment e.g. by means of hydraulic actuators.

1. Method of handling wind turbine blades, said method comprising:providing a lifting system including at least one gripping unit forhandling wind turbine blades, said unit comprising gripping means with acurved surface adapted to a shape of a wind turbine blade, gripping atleast one wind turbine blade with said lifting system by connecting thegripping means to the wind turbine blade, and lifting the at least onewind turbine blade with the lifting system.
 2. Method according to claim1, wherein the gripping unit performs the gripping by forcing a numberof clamping jaws against sides of the wind turbine blade in at least twolifting positions.
 3. Method according to claim 1, wherein the grippingunit grips a wind turbine blade in at least two lifting positions, saidlifting positions being symmetrically positioned around a center pointof said wind turbine blade.
 4. Method according to claim 1, wherein saidat least one wind turbine blade is controlled by one or more wiresconnected to at least one crane or to one or more winches.
 5. Grippingunit for handling a wind turbine blade, said unit comprising grippingmeans having a curved surface adaptable to a shape of specific types ofwind turbine blades and comprising at least two gripping points forengaging with surfaces of said wind turbine blades.
 6. Gripping unitaccording to claim 5, wherein said gripping means is changeable from onesize to another.
 7. Gripping unit according to claim 5, wherein saidgripping means includes at least one adjustable clamping jaw connectedto a hydraulic, an electric or a pneumatic system for steplessadjustment of a position of the clamping jaw in relation to said windturbine blade and at least one fixed clamping jaw, said jaws forming aclamping jaw set.
 8. Gripping unit according to claim 7, wherein saidgripping means includes two sets of said clamping jaws for engaging withthe surface of said wind turbine blade, said sets being adapted to agiven wind turbine blade type.
 9. Gripping unit according to claim 7,wherein said clamping jaws include a friction surface layer. 10.Gripping unit according to claim 9, wherein said friction surface layercomprises vulcanized rubber.
 11. Gripping unit according to claim 9,wherein said friction surface layer comprises at least one tread patternincluding one or more dents.
 12. System for handling wind turbineblades, wherein said system comprises a gripping unit according to claim5 and a lifting system.
 13. System for handling wind turbine bladesaccording to claim 12, wherein said lifting system includes a crane witha number of wires lifting and controlling said gripping unit.
 14. Systemfor handling wind turbine blades according to claim 12, furthercomprising at least one additional wire controlling at least one windturbine blade is connected to said blade with connection meanscomprising a flexible cuff or a similar flexible band surrounding a partof a tip of said blade.